1. Field of the Invention
The present invention is directed to a hydrodynamic device comprising at least one vane wheel arranged in a housing cover and rotatable about an axis of rotation and a work fluid in the housing cover which can be driven to movement by the at least one vane wheel.
2. Description of the Related Art
A hydrodynamic device in the form of a hydrodynamic torque converter provided with a throttle element which is displaceable by the application of pressure for changing the converter characteristic is known from German reference DE 197 36 297 A1. The throttle element is selectively displaceable between an advanced position in which a throttle projection of the throttle element is engaged in the fluid circulation in the region of the impeller wheel and a retracted position in which there is essentially no such engagement. When the throttle projection is advanced into the fluid circulation, the fluid circulation is impeded so that the fluid-dynamic coupling between the impeller wheel and the turbine wheel is at least reduced. This state is occupied particularly when the driving unit is started, so that the energy required for starting the driving unit is reduced by the at least partly decreased or absent output transmission capacity of the torque converter. In normal converter operation, the throttle element is retracted to unblock the fluid circulation so that the converter accordingly realizes its function for transmitting and converting the torque introduced from the driving unit.
The construction of this known hydrodynamic torque converter is relatively complicated because it requires a throttle element that is displaceable even when the fluid pressure in the interior of the converter is relatively high and it requires control lines for the throttle element. Further, since this known device requires an additional component which is mechanically displaceable during operation must be provided, i.e., the throttle element, the risk of malfunction, for example, when the throttle element jams as a result of vibrations, is increased over a torque converter without the throttle element.
It is the object of the present invention to provide a hydrodynamic device by which the flow behavior of a work fluid contributing to the transmission of torque can be influenced in a reliable manner.
According to the present invention, the object is met by a hydrodynamic device comprising at least one vane wheel arranged in a housing cover and rotatable about an axis of rotation and a work fluid in the housing cover that can be driven to circulation by the at least one vane wheel within the housing cover. The hydrodynamic device preferably comprises at least two vane wheels.
The work fluid is electrically conductive. The hydrodynamic device further comprises a magnetic device for generating a magnetic field in the area of the work fluid circulation within the housing cover and an electric device for generating an electric current flow through the work fluid.
In such an arrangement of a hydrodynamic device according to the present invention, a Lorentz force is generated by the interaction of the magnetic field and the electric current flowing through the magnetic field. Since the electric current flow is through the work fluid, the Lorentz force also acts on the work fluid. Accordingly a force may be generated with respect to the existing or planned flow direction of the work fluid circulation for accelerating or retarding the work fluid circulation depending on the direction of the magnetic field and on the direction of the electric current flow. When the hydrodynamic device comprises a plurality of vane wheels such as, for example, in a hydrodynamic torque converter, the acceleration or retardation of the work fluid circulation ultimately changes the characteristics of the hydrodynamic device.
The direction of the magnetic field and electric current flow may be suitably selected to act on the work fluid in a deliberate manner to reduce the fluid-dynamic coupling between two vane wheels, for example, in a hydrodynamic coupling or a hydrodynamic converter. That is, the magnetic field and electric current flow may be selected to generate a Lorentz force which impedes the work fluid circulation, i.e., brakes the work fluid. When a Lorentz force is generated which is directed in the fluid flow direction, the work fluid is accelerated, which produces a stronger fluid-dynamic coupling and therefore an improved torque transmission between two vane wheels. The acceleration of the work fluid for strengthening the fluid-dynamic coupling cannot be achieved with the mechanically displaceable throttle element known from the prior art. Further, the hydrodynamic device according to the present invention may also be used as a drive unit because, for example, the Lorentz force may be generated for setting the work fluid in circulation even when the impeller wheel is stopped so that the turbine wheel is driven in rotation solely by the generation of the Lorentz force.
The direction of the electric current flow in at least one area is not parallel to and is preferably substantially orthogonal to the direction of the magnetic field so that the interaction between the magnetic field and the electric current flow may be utilized with high efficiency in the hydrodynamic device according to the present invention.
The arrangement of the direction of the magnetic field non-parallel to and preferably substantially orthogonal to the work fluid flow direction in the at least one area also facilitates a high efficiency in influencing the flow characteristic of the work fluid. Further, the direction of the electric current flow in the at least one area is not parallel to and is preferably orthogonal to a direction of work fluid flow in the area.
High efficiency in the generation and transmission of torques may also be achieved in that at least one of the vane wheels has a plurality of vanes following one another in the circumferential direction.
Since fluid circulation takes place along an intermediate space between successive vanes in the circumferential direction in an arrangement of plural vanes arranged in succession in the circumferential direction, it is further suggested according to the invention that the magnetic field extends in the area between at least two of the plural vanes of at least one vane wheel.
The intermediate space between two vanes may be utilized in the best possible manner for the above-mentioned generation of Lorentz force for accelerating or retarding the work fluid when the magnetic field extends from one of the at least two vanes to the other of the at least two vanes. For this purpose, means for generating the magnetic field may be provided in at least one of the vane wheels in the area of at least one vane, and are preferably provided in a plurality of vanes or all the vanes of the at least one vane wheel.
A simple arrangement for generating the magnetic field, for example, comprises providing at least one vane that is permanently magnetic. Of course, a plurality of the vanes or all the vanes of a vane wheel may be permanently magnetic. Instead of a permanent magnet, a vane may be arranged for generating a magnetic field by an electric current flow.
Further, it is preferably provided in the hydrodynamic device according to the present invention that at least one of the vane wheels has an outer vane wheel element and an inner vane wheel element. The presence of the inner and outer vane wheel elements is preferably made use of, according to the present invention, so that the electric device for generating an electric current flow through the work fluid is arranged for generating an electrical potential difference between the outer vane wheel element and the inner vane wheel element of the at least one of the vane wheels. Accordingly, existing subassemblies or components in a vane wheel may be used additionally to form the potential difference, thereby obviating the need to add separate structural component parts or subassemblies for affecting the work fluid flow.
To enable the electric current flow through the work fluid, the outer vane wheel element and the inner vane wheel element are in electrically conducting contact with, or can be brought into electrically conducting contact with, the work fluid at least in some areas. In this regard, it is noted that the direction of the electric current flow between the outer vane wheel element and the inner vane wheel element, and therefore the resulting Lorentz force and its direction, may be influenced by suitable selection of the areas of the inner and outer vane wheel elements which are arranged for electrically conducting contact with the work fluid.
It is further suggested that the outer vane wheel element and the inner vane wheel element are connected or can be connected with an electric power supply source by electric line arrangements in the at least one vane wheel.
In an alternative embodiment form of the hydrodynamic device according to the present invention, the magnetic field may extend in the area between the outer vane wheel element and the inner vane wheel element of at least one of the vane wheels. In this embodiment, all of the space available for the movement of the work fluid between the outer vane wheel element and the inner vane wheel element may be utilized for generating the electromagnetic interaction when the magnetic field extends from the outer vane wheel element to the inner vane wheel element, or vice versa.
In this case, an arrangement for generating the magnetic field is preferably provided at the outer vane wheel element and/or the inner vane wheel element, wherein, for example, the outer vane wheel element and/or inner vane wheel element may again be permanently magnetic.
In this embodiment in which the magnetic field extends substantially between the outer vane wheel element and the inner vane wheel element, or vice versa, the device is constructed for generating the electric current flow through the work fluid to generate an electric potential difference between at least two vanes in at least one of the vane wheels for generating a Lorentz force with high efficiency. This arrangement produces an electric current flow direction that runs essentially orthogonal to the magnetic field direction. Further, the resulting Lorentz force is parallel to the movement direction at least in areas of the direction of movement of the circulating work fluid.
In this connection, it is further suggested that the at least two vanes are in electrically conducting contact with, or can be brought into electrically conducting contact with, the work fluid at least in some areas and that the at least two vanes are connected with, or can be connected with, an electric power supply source by electric line arrangements.
To ensure that the current flow occurs between desired areas and that no short circuiting occurs through other components of the hydrodynamic device, at least a portion of the vanes are electrically insulated with respect to the outer vane wheel element and the inner vane wheel element.
As mentioned above, the at least one vane wheel of the hydrodynamic device according to the present invention may comprise at least one impeller wheel and at least one turbine wheel when the hydrodynamic device comprises a torque converter or coupling. If the hydrodynamic device is also to perform the function of efficient torque conversion, it is advantageous when the at least one vane wheel of the hydrodynamic device according to the invention further comprises at least one stator wheel.
When the hydrodynamic device comprises a turbine wheel and an impeller wheel, the magnetic field and the electric current flow through the work fluid are generated in the area of the at least one impeller wheel and/or in the area of the at least one turbine wheel. Since the impeller wheel in such devices generally forms an outer shell, it is advantageous to generate the magnetic field or the current flow in the area of the impeller wheel because it is easier to feed electric lines thereto.
However, it is also possible to generate the magnetic field and the current flow through the work fluid in the area of the at least one stator wheel in a hydrodynamic torque converter.
To minimize electrical losses for efficiently influencing the flow behavior of the work fluid, the work fluid comprises a specific resistance in the range of 10xe2x88x927 m to 100 m.
For example, the work fluid may comprise water, preferably the cooling water of a drive unit or a coolant of a drive unit. Alternatively, the work fluid may also comprise an acid, preferably sulfuric acid, or a lye.
As was already mentioned, the hydrodynamic device according to the present invention may be constructed as a hydrodynamic coupling device and preferably comprises a hydrodynamic torque converter or fluid coupling.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.